How the grout calculator works
Grout fills the channels between tiles, so the amount depends on the total length of joint in each square metre and on the cross-section of that joint. Small tiles create far more joint length than large ones: a square metre of 10 × 10 cm tiles contains 20 m of joint, while a square metre of 60 × 60 cm tiles contains only 3.3 m.
kg per m² = (A + B) ÷ (A × B) × C × D × 1.6Here A and B are the tile length and width in millimetres, C is the joint width and D the joint depth, also in millimetres. The first part gives litres of joint per square metre; multiplying by 1.6, the typical density of mixed cement grout in kg per litre, converts it to weight. The calculator then multiplies by the area and adds 10% for material left on the float, in the bucket and on the sponge.
Worked example
A 12 m² floor is laid with 60 × 30 cm porcelain tiles, 9 mm thick, on 3 mm spacers. The joint factor is (600 + 300) ÷ (600 × 300) = 0.005, so each square metre holds 0.005 × 3 × 9 = 0.135 L of grout, or 0.135 × 1.6 = 0.216 kg. Over 12 m² that is 2.59 kg, and 2.85 kg once the 10% margin is included. A single 5 kg bag is enough, with some left for later repairs. The same floor on 5 mm joints would need 4.75 kg, still one bag but only just.
Grout consumption for common tile formats
| Tile size | Joint width | Joint depth | Grout (kg/m²) |
|---|---|---|---|
| 2.5 × 2.5 cm mosaic | 2 mm | 4 mm | 1.02 |
| 10 × 10 cm wall tile | 2 mm | 6 mm | 0.38 |
| 20 × 20 cm | 4 mm | 8 mm | 0.51 |
| 30 × 30 cm | 3 mm | 8 mm | 0.26 |
| 30 × 60 cm | 3 mm | 9 mm | 0.22 |
| 33 × 33 cm terracotta | 8 mm | 12 mm | 0.93 |
| 60 × 60 cm | 2 mm | 10 mm | 0.11 |
| 60 × 120 cm | 2 mm | 10 mm | 0.08 |
To convert, 1 kg per m² equals about 20.5 lb per 100 ft². Mosaic sheets and handmade terracotta use by far the most grout, which is why a small shower wall in mosaic can need more material than a whole kitchen in large porcelain.
Choosing and using grout
- Sanded or unsanded. Unsanded grout is meant for joints narrower than about 3 mm (1/8 in); sanded grout resists shrinking and cracking in wider joints. Check the joint range printed on the bag.
- Epoxy grout. It is stain-proof and suits showers and kitchen worktops, but its density and working time differ, so use the coverage chart of the product rather than the 1.6 factor.
- Measure the real depth. Rake out excess tile adhesive from the joints before it sets. A joint that is only half filled with grout is weaker and will crack under foot traffic.
- Mix in batches. Mix only what you can apply and clean in 20–30 minutes, and keep the same water ratio for every batch so the colour stays even.
- Movement joints. Leave perimeter and movement joints free of grout and fill them with a flexible sealant instead, as tiling standards require.
Frequently asked questions
How much grout do I need per square metre?
For 30 × 30 cm floor tiles with a 3 mm joint and 8 mm thickness, about 0.26 kg per m². Large 60 × 60 cm tiles need around 0.1 kg per m², while small mosaics can need 1 kg per m² or more.
How many square feet does a 25 lb bag of grout cover?
It depends mostly on tile size. With 12 × 24 in tiles, 3/8 in thick, on 1/8 in joints, 25 lb covers roughly 470 ft²; with 1/4 in thick 4 × 4 in wall tiles on the same joints it covers only about 175 ft².
Is a 5 kg bag of grout enough for a bathroom?
For a floor of 5 m² with 30 × 30 cm tiles you need about 1.4 kg, so yes. A tiled shower in 2.5 cm mosaic uses around 1 kg per m², so 5 kg covers about 4.4 m² of walls.
How deep should grout be?
Grout should fill the joint to the full depth of the tile, or at least two-thirds of it. Clean out adhesive before it hardens so there is room for the grout.
Can I use unsanded grout for 1/8 inch joints?
Unsanded grout is usually rated for joints up to 1/8 in (3 mm). For anything wider, use sanded grout, which shrinks less and does not crack as easily.
Last reviewed: 2026-09-27 · How we calculate